Electrokinetic sample injection for high‐sensitivity CZE (part 2): Improving the quantitative repeatability and application of electrokinetic supercharging‐CZE to the detection of atmospheric electrolytes

Abstract

Electrokinetic supercharging (EKS) is defined as a technique that combines electrokinetic sample injection with transient ITP. Quantitative repeatability of EKS-CZE and the other CE methods using electrokinetic sample injection process is usually inferior in comparison with the CE methods using hydrodynamic or hydrostatic injection. This is due to some effects, such as the temperature change and the convection of the sample solution in the reservoir, as well as the change of the distance between an electrode and a capillary end (D(ec)). In particular, we have found that the D(ec) change might most seriously affect the repeatability, especially when the electrode is a thin Pt wire that could be unintentionally bent during sampling. By using a Teflon spacer to fix D(ec) to 1.1 mm, the RSD of peak area (n=5) was decreased from 20 to 3.4% in EKS-CZE for several metal cations. This D(ec) dependence of the sample amount injected was supported by computer simulation using CFD-ACE+ software. The improved repeatability (down to 5.1% at n=5, averaged RSD for Co(2+), Li(+), Ni(2+), Zn(2+) and Pb(2+)) was also experimentally attained by increasing the D(ec) to ca. 20 mm, which was also effective to obtain high sensitivity. Since the temperature and the convection effects on the repeatability are comparatively small in a proper laboratory environment, these effects were estimated from the EKS-CZE experiments using conditions such as warming and agitating the sample solution during EKS process. Finally, EKS-CZE was applied to the detection of ions from atmospheric electrolytes in high-purity water exposed to ambient air for 2 h. The microgram per liter levels of anions (chloride, sulfate, nitrate, formate, acetate and lactate) and cations (ammonium, calcium, sodium and magnesium) could be detected using conventional UV detector.

Electrokinetic supercharging with a system‐induced terminator and an optimized capillary versus electrode configuration for parts‐per‐trillion detection of rare‐earth elements in CZE

“…In its basic design, EKS lowered the LOD of Er down to 0.27 mg/L (1.6 nM) [11]. The following studies demonstrated that the electrode configuration and position significantly affect the efficiency and reproducibility of sample injection [16,17]. Importantly, by increasing the distance between tips of the electrode and the capillary in vertical direction (abbreviated as D e/c hereafter), which are located in a typical sample vial, the LOD of erbium was improved to an impressive threshold of 0.02 mg/L (0.12 nM) [16].…”

Simultaneous Determination of Pyridine-Triphenylborane Anti-Fouling Agent and Its Degradation Products in Paint-Waste Samples Using Capillary Zone Electrophoresis with Field-Amplified Sample Injection

“…Using a long Dec (8 mm), the peak heights for PTPB and DPB were, respectively, 2.2 and 1.2 times higher than those obtained using the default Dec (0.5 mm). The peak heights for MPB and phenol were, respectively, 0.41 and 0.40 times lower than those obtained using the default Dec. Hirokawa et al 38 determined atmospheric electrolytes using EKS-CZE with a default Dec (1.1 mm) and a long Dec (19.5 mm). The LODs obtained using the long Dec were improved ca.…”

“…The analytical conditions, time of water plug injection, time, and voltage of sample introduction were examined and optimized. Boer and Ensing, 36 and Hirokawa et al 37,38 reported that the efficiency of EKI and EKS is strongly related to the electrode configurations. Therefore, we investigated the effects of the distance between the tip of the electrode and a capillary end (Dec) on the peak heights for the analytes listed above using FASI.…”

High‐sensitivity capillary and microchip electrophoresis using electrokinetic supercharging

“…Following this work, the authors provided a new strategy for viable improvement in the quantitative repeatability of EKS [52]. They proposed that variation in the distance between the electrode and the capillary end will adversely affect the quantitative repeatability of any EKI procedure.…”